A Torques in a pump

Hi
In a pump (which operates in normal condition: steady state), pump torque is positive and fluid torque is of equal magnitude and of opposite direction so that the sum of both is zero. ''P. 66 of 'Water Hammer: An Analysis of Plumbing Systems, Intrusion, and Pump Operation' by: Dr. Loganathan and ...
I need so explanation about opposite sign of pump torque and fluid torque? Both rotate in a same direction, then why one of positive and the other is negative?

Staff: Mentor

The force from the water on the pump is equal to the force from the pump on the water, but in the opposite direction. Because it is in the opposite direction, the direction of torque is also opposite, hence the negative sign.